Backflow prevention assembly

ABSTRACT

A backflow prevention assembly has a unitary housing with a passage therethrough, two threaded regions formed in an inner surface of the unitary housing, and two valve assemblies positioned in the passage to prevent fluid flow in a direction. Each valve assembly has an annular mount having a threaded outer surface that engages one of the threaded regions on the inner surface of the housing. The threads can be formed by placing a die having a thread on an outer surface thereof in contact with an inner surface of the unitary housing, and pressing on the outer surface of the housing.

BACKGROUND

This invention relates to a backflow preventer.

Backflow preventers are principally to prevent contamination of a publicwater distribution system by reducing or eliminating backflow orback-siphonage of contaminated water into the system.

Usually, the backflow prevention assembly is installed in a pipelinebetween a main supply line and a service line that feeds aninstallation, e.g., a hotel, factory or other institution, or even amultiple or single family residence. A backflow prevention assemblytypically includes two check valves that are configured to permit fluidflow only in the direction from the main supply line to the serviceline.

FIG. 1 illustrates a conventional connection between a valve module 40′and a housing 20′ of a prior art backflow preventer. As shown, anannular mount 90 having an threaded inner surface 92 and a smooth outersurface 94 is secured to a cylindrical inner surface 96 of housing 20′,e.g., by solder 98 or welding 99. The valve module 40′ is then screwedinto mount 90 to secure it to the housing.

SUMMARY

In one aspect, the invention is directed to a backflow preventionassembly. The backflow prevention assembly has a unitary housing with apassage therethrough, two threaded regions formed in an inner surface ofthe unitary housing, and two valve assemblies positioned in the passageto prevent fluid flow in a direction. Each valve assembly has an annularmount having a threaded outer surface that engages one of the threadedregions on the inner surface of the housing.

Implementations of the invention may include the following features. Thetwo valve assemblies may be cam-check valves. The threaded regions maybe formed by a thread rolling process, e.g., by placing a threaded dieagainst the inner surface of the housing and pressing on an outersurface of the housing. Threaded regions may also be formed in the outersurface of the unitary housing.

In another aspect, the invention is directed to a method of formingthreads in a tubular housing. In the method, a die having a thread on anouter surface thereof is placed in contact with an inner surface of aunitary housing having a passage therethrough. The outside of thehousing is pressed to drive the inner surface against the threads on theouter surface of the die to form threads on the inner surface of thehousing.

Implementations of the invention may include the following features. Thethread on the outer surface of the first die may be generally theinverted shape of the threads to be formed on the inner surface of thehousing. A second die having a thread formed on an outer surface thereonmay be used to press on the outside of the housing. Two valve assembliesmay be positioned in the passage to prevent fluid flow in a direction,each valve assembly having an annular mount having a threaded outersurface that engages one of the threaded regions on the inner surface ofthe housing. A port may be formed in a wall of the housing.

Advantages of the invention may include the following. The backflowprevention assembly is easier to assemble, e.g., in the field, and isless expensive to manufacture than currently available backflowprevention assemblies for similar applications.

Other features and advantages of the invention will become apparent fromthe following detailed description, including the drawings and theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a conventional connection between a check valve and ahousing in a prior art backflow preventer.

FIG. 2 is a cross-sectional view of a backflow prevention assemblyaccording to the present invention.

FIG. 3 is a cross-sectional view of a check valve from the backflowpreventer of FIG. 2.

FIG. 4 is a cross-sectional side view illustrating the formation of thethreads in the housing of the backflow preventer.

FIG. 5 is a view along line 5—5 of FIG. 4.

FIG. 6 is an expanded view of the connection of the check valve to thehousing

in the backflow preventer of FIG. 2.

DETAILED DESCRIPTION

Referring to FIG. 2, a backflow prevention assembly 10 includes aunitary tubular housing 20 having a first end 22 and a second end 24. Athrough bore 26 extends between the ends 22, 24 of housing 20 for theflow of water therethrough. A pair of valve modules 40, 60 are locatedinside through bore 26 to permit fluid flow from the first end 22 ofhousing 20 to the second end 24 of housing 20, while preventing fluidflow in the opposite direction. An inner surface 28 of tubular housing20 includes two threaded annular regions 30, 32 with internal threads34, 36.

Valve module 40 may be a cam-check valve, e.g., Check Assembly Kit No.RK-775CK1 available from Watts Industries, North Andover, Mass.,although the invention is applicable to other valves, such as a ballvalve. As shown in FIG. 3, cam-check valve 40 includes an annular seat42, a clapper 44 pivotally connected to annular seat 42, and a cam arm46 to prevent over-extension of clapper 44. An outer surface 48 of seat42 includes external threads 54 and an annular recess 50 to secure anO-ring 52 near an end 56 of the seat adjacent clapper 44. When valvemodule 40 is inserted into through bore 26, external threads 54 on seat42 cooperate with threads 34 in threaded annular region 30 to securevalve module 40 in housing 20. In addition, O-ring 52 is secured betweenouter surface 48 of seat 42 and housing 20 to prevent fluid leakagetherebetween. A similar cam-check valve, lacking external threads and anannular recess for an O-ring on the outer surface of the seat, isdescribed in U.S. Pat. No. 5,855,224, the entirety of which isincorporated herein by reference.

Returning to FIG. 2, valve module 60 can also be a cam-check valve, andcan be constructed in a fashion similar to valve module 40 with anannular seat 62, a clapper pivotally connected to annular seat 62, and acam arm to prevent over-extension of clapper. An outer surface of theseat includes external threads 64 and an annular recess 66 to hold anO-ring 68. External threads 64 cooperate with internal threads 36 tosecure valve module 60 in housing 20. Like valve module 60, O-ring 68 issecured between the outer surface of seat 62 and housing 20 to 20prevent fluid leakage therebetween. However, in valve module 60, annularrecess 66 can be located near an end 58 of seat 62 opposite clapper 60.

Housing 20 includes a port 70 which provides access to bore 26 and valvemodules 40 and 60. Port 70 is closed by securing a cover plate 72 to arim 74 with a groove coupler 76 and a groove coupler gasket 78.

Referring to FIGS. 4 and 5, threads 34, 36 are formed in housing 20 by athread rolling process that uses a threaded internal die 80. Internaldie 80 has threads 82 that are the inverse shape of the threads to beformed on housing 20. Unlike conventional thread rolling processes, inwhich a die with non-inverted threads is held against the outsidesurface of a housing, in this method, internal die 80 is held againstinside surface 28 of housing 20. Specifically, housing 20 begins with aninner diameter D1 that is slightly larger than the major diameter D2 ofthreads 82 on internal die 80. The threaded internal die 80 is insertedinto through bore 26, and external die 84 are positioned around an outersurface 29 of tubular housing 20. The external die force a portion 30 oftubular housing 20 inwardly to mold inner surface 28 of housing 20 tointernal die 80, thereby forming threads 34. Alternatively, tubularhousing 20 can be held steady and internal die 80 can be moved in anorbit as it is pressed against the inner surface of the housing. Ineither case, the threads penetrate the blank inner surface to form thethread roots and displace material radially outward to form the diecrests. Then the internal die is unscrewed from threaded portion 30 toremove the internal die from the housing. This thread rolling process isthen repeated form threads 36 in threaded portion 32 of housing 20.

Alternatively, two die could be inserted into the through bore, andthreaded portions 30 and 32 could be formed simultaneously. In addition,the external die 84 can have a thread 86 formed on its outer surface toforce the material of the housing into the gaps between threads 82 oninternal die 80, thereby also forming threads on outer surface 29. Theport 70 could be formed in housing 20 before or after threaded portions30 and 32.

Since the inner surface of the housing directly contacts the die, thethreads more closely match the shape intended by the die than if the adie with non-inverted threads was pressed against the outside surface ofthe housing. In contrast to other thread forming processes, such asgrinding, thread rolling does not remove metal. In addition, the coldforming process can strengthen the threads by work hardening and formreinforcement.

As previously discussed, in the conventional backflow preventer shown inFIG. 1, the threads are formed in a mount that is soldered to thehousing. In contrast, as shown in FIG. 6, threaded portions 30 and 32are formed directly on inner surface 28 of unitary housing 20, and valvemodule 40 is secured directly to housing 20, without an interveningmount or soldering, thereby decreasing the time and expense inconstructing the backflow prevention assembly 10.

The invention has been described in terms of a preferred embodiment.Other embodiments are within the scope of the claims.

What is claimed is:
 1. A backflow prevention assembly, comprising: aunitary housing having a wall defining a passage therethrough; twothreaded regions formed in an inner surface of the unitary housing byreshaping the wall of the unitary housing; and two valve assembliespositioned in the passage to prevent fluid flow in a direction, eachvalve assembly having an annular mount having a threaded outer surfacethat engages one of the threaded regions on the inner surface of thehousing.
 2. The backflow prevention assembly of claim 1, wherein the twovalve assemblies are cam-check valves.
 3. The backflow preventionassembly of claim 1, wherein the threaded regions are formed by a threadrolling process.
 4. The backflow prevention assembly of claim 1, whereinthe threaded regions are formed by placing a threaded die against theinner surface of the housing and pressing an outer surface of thehousing.
 5. The backflow prevention assembly of claim 1, furthercomprising threaded regions formed in the outer surface of the unitaryhousing. a wall of the housing.
 6. The backflow prevention assembly ofclaim 1, wherein the wall defines the passage in a straightconfiguration.
 7. A backflow prevention assembly, comprising: a unitaryhousing having a passage therethrough; two threaded regions formeddirectly in an inner surface of the housing by placing a die having athread on an outer surface thereof in contact with the inner surface ofthe housing and pressing on the outside of the housing to drive theinner surface against the threads on the outer surface of the die; andtwo valve assemblies positioned in the passage to prevent fluid flow ina direction, each valve assembly having an annular mount having athreaded outer surface that engages one of the threaded regions on theinner surface of the housing.